Its all about footprint, if you had said a 90 L (6ft) your options might be slightly more varied, but to me a pair that maxes out at 9" is as far as I would push the limit of a 90 standard. And even then I'd have a divider at the ready, to drop in, to protect the female.
The standard footprint (IMO) leaves out any Parachromis, or similar species, like grammodes, and also leaves out any of the Vieja genus.
Amatitlania, Thorichthys, or others of that less territorial temperament would be better choices (maybe a pair of bartoni).
And if it were me, I'd start with a group juvies (6-8) and allow them to determine their own pair. In that way, it will be obvious, and by letting them select on their own, that pair bond could be more tightly knit.
If you were to opt for the more bellicose species (like grammodes), also start with juives, but expect the pair to kill off any others that don't make the muster .
I had grammodes years back, bought half dozen 2" juvies, grew them out in a similar footprint tank to yours, by the time they were 4" a pair had formed, and killed off all others, they spawned 3 times, so I thought they were bonded enough, but the male killed the female one night.
Even 6 ft tanks are quite tiny compared to natural habitat for aggressive territorial types.
Most cichlids make 4 ft, a territorial boundary, and only break off chase at that point, so even a 6ft tank offers little extra space once a males territory has been determined.